A student approached me claiming to have an ability that she described as a “sixth sense”. She claimed to be able sense things about people that she could not see. She gave an example of meeting an acquaintance and sensing that he had been in a car accident even though she could not see any visible signs of the accident.

We started by attempting to duplicate this phenomenon in a controlled setting. Observers were shown two photographs of the same person, one after the other. On being presented with the second photograph observers were first asked whether the person’s appearance had changed and, if they said it had, they were then presented with a list of possible changes and asked to select from this list the change that had occurred.

We found that people could reliably sense when a change had occurred even when they could not identify what had changed and consequently believed that they had not seen the change. In other words they often sensed changes that they thought they had not seen, just like the original student.

We then investigated the mechanism underlying this sensing ability using images similar to abstract modern art paintings. We found that it was due to observers subconsciously monitoring the global properties of the images, such as the total amount of red or green in each image.

Our research was the first to show that people can reliably sense changes that they believe that they can not see but it also showed that this was due to known sensory mechanisms and was not evidence for a “sixth sense”.